[olddog]

Some where in this thread someone mentioned that what pressure leaks past the first compression ring is trapped by the second compression ring. If I recall correctly they said something to the affect of the pressure trapped between the two rings, pushes the top ring off the land causing it to flutter and loose it's seal. Maybe they didn't exactly say this, but it was how I interpreted what ever was said. I think this is along the lines of what Barry_R is talking about.

What about using one gap-less and one normal compression ring? Has this been tried? I'm not sure if the top should be the gap-less or not, but it would seem the logical place.